Va. Code Ann. § 20-88.74

A party or support enforcement agency seeking to modify, or to modify and enforce, a child support order issued in another state shall register that order in this Commonwealth in the same manner as provided in Article 8 (§ 20-88.66 et seq.) if the order has not been registered. A petition for modification may be filed at the same time as a request for registration, or later. The pleading must specify the grounds for modification.